2006 g3 angler v165 with 115 hp 2 stroke

i just bought this boat and was wondering what is the original prop that came with that 2 stroke motor.iam am getting 37, 38 mph on the gps with a 13.25 diameter 17 pitch.i think i should get at least 40 mph any idea ?i also got a 13.5 diameter 19 pitch stainless witch i get basically the same speed but lost 900 rpm.

[boats.net]

The wide open rpm range on that motor is 4500-5500 rpm's. The larger the pitch on a prop is less rpm's and more mph but too much pitch will drop it below rpm range and will loose mph.